Energy production requires state-of-the-art monitoring systems. Of course, these systems require energy of their own to operate. For example, GE Energy recently developed a system that monitors machinery conditions for a field trial at the Nyhamna gas plant in Norway. By harvesting the vibration energy from the machines it monitors, this system’s power supply is inexhaustible.
This power supply uses a microgenerator to convert vibrational energy into usable electrical energy. It then stores that energy in a supercapacitor; therefore, enough is available for the higher-power bursts to measure and transmit condition-monitoring data to a basestation.
CONDITION MONITORING
Plants and refineries monitor both machines and processes to ensure optimum safety, up-time, and efficiency. Machinery condition monitoring involves measuring the vibrational spectrum of rotating machinery, such as pumps, motors, and turbines, to determine their health. Rotational speed and shaft/bearing construction determine the frequency of vibration. The amplitude of vibration indicates machine health.
For instance, smooth-running machines have low amplitude vibration, while defects in bearing surfaces and/or unbalanced or misaligned shafts increase the amplitude of vibration. As the problems worsen, the amplitude increases. Thus, frequent monitoring of vibration frequency and amplitude reveals problems as they occur to help engineers predict when it’s most economical to take equipment offline for maintenance.
Plants will instrument and do the wiring for turbines, critical high-capacity pumps, motors, and the like when installed. But it isn’t cost-effective to do this for the “balance of plant,” including the less-critical pumps, motors, and compressors that abound in oil refineries, gas plants, and mineral processing plants.
If one of these less-critical pieces of machinery fails unexpectedly, the plant may incur significant costs in lost production and emergency maintenance. Typically, maintenance engineers monitor “balance of plant” by walking around with a vibration transducer and laptop to periodically inspect equipment, the frequency of which is determined by the criticality of the equipment.
It would be far more convenient if a low-cost system consisting of a vibration sensor, microcontroller, and radio transmitter was fitted to the balance of plant, which could periodically report the vibration spectra to a maintenance basestation. The question then becomes how to power these remote sensors.
A PERPETUAL POWER SUPPLY
Batteries could power the remote sensors. However, batteries may survive only two to five years in such harsh environments. So, in plants with hundreds or thousands of battery-powered wireless sensor nodes, the cost of monitoring, replacing, and recycling them is significant.
Given we are monitoring rotating machinery, it’s guaranteed that vibrational energy will be available. Hence, the most natural and attractive solution is to capture this vibrational energy to power the remote condition-monitoring sensors, thereby providing a free, perpetual power supply.
This power supply includes two critical components. First, a PMG17 microgenerator from Perpetuum can harvest even very low levels of vibrational energy from a smooth-running piece of equipment (Fig. 1). Second, a supercapacitor from CAP-XX can store this energy and release it in short, high-power bursts to read and transmit the condition monitoring data.
VIBRATION ENERGY HARVESTER
The PMG17 is an inductive energy harvester with an optimized magnetic circuit coupled to a magnetic resonator designed for ac motors. It harvests the commonly found “twice the line frequency vibration.” Therefore, the unit is tuned to 100 Hz for a 50-Hz ac supply or to 120 Hz for a 60-Hz ac supply.
Also, the PMG17 is highly efficient. With as little as 25-mg RMS vibration within a 2-Hz bandwidth, it will produce a minimum power output of 0.5 mW (Fig. 2). If a unit is tuned to 120 Hz to harvest energy from a 60-Hz ac motor, then the output power would be 1 mW if there is 25 mg of vibration at 120 Hz, 0.6 mW if there is 25 mg of vibration at 119 Hz, 1 mW if there is 50 mg of vibration at 122 Hz, and so on.
The microgenerator is a high-impedance voltage source (Fig. 3). The power-conditioning and storage block should control the current drawn from the microgenerator to maintain its output voltage at approximately 5 V to maximize the power transferred from it. This current level will be approximately 120 µA.
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